The development of New Radio (NR) systems, e.g., coordinated by the International Telecommunication Union (ITU) and the Third Generation Partnership Project (3GPP), is led by overall requirements for the Next Generation (NG) architecture (e.g., according to the document TR 23.799, “Study on Architecture for Next Generation”) and more specifically for the NG Access Technology (e.g., according to the document TR 38.913, “Study on Scenarios and Requirements for Next Generation Access Technologies”; and document RP-160671, “New SID Proposal: Study on New Radio Access Technology”, DoCoMo), which require new mechanisms for the mobility of a radio device connected to such NR systems compared to the current mobility solution in 3GPP Long Term Evolution (LTE). Some of these requirements include supporting network energy efficiency mechanisms and a very wide range of frequencies (e.g., up to 100 GHz).
In conventional LTE systems, a user equipment (UE) is capable of detecting synchronization signals transmitted from any cell within range and measure reference signals (RSs) from same cell assuming that the transmission of the synchronization signal and the transmission of the associated RSs from the same cell are synchronized and time-aligned. That is, by virtue of this self-contained cell discovery, the UE is able to perform blind detection, identification and measurement of any cell.
For LTE handover, the UE reports discovered cells to the serving cell currently connected to. A cell identity, i.e. the physical cell identifier (PCI) acquired by the UE from primary and secondary synchronization signals of the discovered cell, and a carrier frequency are stored at the evolved Node B (eNB) of the serving cell for table look-up when determining a target cell detected and reported by the UE. By acquiring the Cell Global Identifier (CGI) or the E-UTRAN CGI (ECGI) of reported candidate cells, the eNB can globally identified the candidate target cells and update its table.
For handover in LTE, the source eNB initializes handover preparation and execution after receiving an event or a report containing the PCI. The source eNB performs the table look-up for translating the PCI to a target eNB and target cell. Handover preparation is initiated by the source eNB by signaling towards the selected target eNB of the target cell. The target eNB assembles a reconfiguration message that the source eNB sends to the UE in a Radio Resource Control (RRC) message. The reconfiguration message contains the mobility command together with information about resources the UE should use in the target cell, such as preamble sequence for random access and Cell-specific Radio Network Temporary Identifier (C-RNTI).
The deployment of a NR system is more flexible than LTE deployment by centralizing upper control protocol layers, e.g. the RRC layer, in a network server (or “cloud”). The lower protocol layers, e.g. the Medium Access Control (MAC) layer, which are more sensitive to delay, are deployed closer to the antenna site to minimize latency, e.g. at a Transmission-Reception Point (TRxP). The NR system may or may not be deployed in cells (“NR cells”). Moreover, the NR cell may include an aggregation of TRxPs. The TRxPs may provide a joint transmission and reception from one or several TRxPs, which may also be geographically distributed.